1. Field of the Invention
The present invention relates to a fiber-optic coil and a method of manufacturing such a fiber-optic coil, and more particularly to a coil of fiber-optic layers wound on a bobbin, for use as the sensor loop of a fiber-optic gyroscope, for example, and a method of manufacturing such a fiber-optic coil.
2. Description of the Prior Art
Fiber-optic sensors find various applications as they are highly sensitive, small in size, light in weight, and highly resistant to environmental changes. One typical use of such a fiber-optic sensor is as a sensor coil in a fiber-optic gyroscope for detecting the angular rate of a moving object. For increased detection sensitivity, the sensor coil comprises a multiplicity of coiled fiber-optic layers that provide an increased area surrounded by the optical fiber. However, it is known that since the optical fiber is coiled in a number of layers, the optical fiber is subject to different temperatures at different portions therealong, resulting in a reduction in the measurement accuracy.
Various methods have been proposed to wind an optical fiber in a symmetric pattern around a coil bobbin for minimizing temperature differences along the optical fiber.
Before a continuous length of optical fiber is coiled around a coil bobbin, it is temporarily wound as first and second segments of equal length on respective supply bobbins, the first and second segments being divided at the center of the optical fiber length.
According to one method, the first optical fiber segment is supplied from its supply bobbin and starts being wound, from the optical fiber center, on a coil bobbin as successive turns from one axial end of the coil bobbin. After a predetermined number of turns of the first optical fiber segment have been wound on the coil bobbin, the second optical fiber segment is supplied from its supply bobbin and starts being wound, from the optical fiber center, on the coil bobbin over the coiled layer of the first optical fiber segment. When the coiled layer of the second optical fiber segment reaches the end of the coiled layer of the first optical fiber segment, the second optical fiber segment starts being wound directly on the coil bobbin axially beyond the coiled layer of the first optical fiber segment.
After a predetermined number of turns of the second optical fiber segment have been wound directly on the coil bobbin, the first optical fiber segment starts to be wound on the coil bobbin over the coiled layer of the second optical fiber segment. In this manner, the first and second optical fiber segments are wound alternately over their coiled layers toward the other axial end of the coil bobbin. After the coil bobbin is fully covered with the first coiled layers, second layers of the first and second optical fiber segments are alternately wound over the first coiled layers toward the starting axial end of the coil bobbin. The above winding process is repeated until the coil bobbin is coiled with a desired number of fiber-optic layers.
According to another winding process, the first optical fiber segment is supplied from its supply bobbin and starts being wound, from the optical fiber center, on a coil bobbin as successive turns from one axial end of the coil bobbin all the way toward the other axial end thereof. After the first optical fiber segment has been wound as a coiled layer on the coil bobbin, the second optical fiber segment is supplied from its supply bobbin and starts being wound, from the optical fiber center, on the coil bobbin over the coiled layer of the first optical fiber segment from the other axial end of the coil bobbin all the way toward the starting axial end of the coil bobbin. When the coiled layer of the second optical fiber segment reaches the starting axial end of the coil bobbin, the second optical fiber segment is wound again over its own coiled layer from the starting axial end of the coil bobbin all the way toward the other axial end thereof.
Thereafter, the first optical fiber segment is wound as two successive layers over the coiled layers of the second optical fiber segment in the same manner as the second optical fiber segment was wound. In this manner, two successive coiled layers of the first optical fiber segment and two successive coiled layers of the second optical fiber segment are alternately wound on the coil bobbin. The above winding process is repeated until the coil bobbin is coiled with a desired number of fiber-optic layers.
However, the conventional winding processes have been complex, time-consuming, and unable to produce fiber-optic coils with a high yield. In addition, since the first and second optical fiber segments are alternately coiled in each fiber-optic layer or different fiber-optic layers, they are twisted and strained, resulting in an undue degradation of their optical propagation characteristics or damage to their own mechanical properties.